Selecting good CCD targets

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This document will describe a procedure for finding good CCD targets for the UMBC telescope.

As an example, we will look for galaxies.

The procedure uses two Unix-based tools available on all JCA Linux ix86 systems including hoth and doron in 306A.

  1. XEphem
  2. SkyCat

These tools may be available for Windows systems. I don't know.

The procedure involves two steps:

  1. Seeing "what's up" in the sky
  2. Checking if they fit well on the CCD frame

For the following, you need to be logged into one of the JCA Linux boxes.

  1. Seeing "what's up" in the sky
    1. Start XEphem:
      xephem &
      or
      /usr/local/bin/xephem &
    2. Set you location to "Baltimore":
      Click on the button below the title, "Local"
      Scroll down to "Baltimore" and select.
      Click on "Set".
    3. Set the local date to when you expect to be taking observations:
      Click on the button to the right of "Local Date"
      Change to the future date. Eg, 11/01/2002
    4. Set the local time to the middle of the evening:
      Click on the button to the left of "Local Time"
      Change to 10 PM: 22:00:00
    5. Update:
      Click on the button labeled "Update"
    6. Take a look at the sky:
      Menu: View -> SkyView
    7. Open the "Sky View Filter":
      "Sky View" window menu: Control -> Filter
    8. Deselect everything:
      Click on the "All" button
      Click on the "Toggle" button
      Click on the "Apply" button
    9. Select all galaxies:
      Under the "Galaxies:" label, click on the "Toggle" button
    10. Set the limiting magnitude for galaxies:
      Slide the "Deep Sky Lim Mag" ruler to the left until it reads "12"
      Click on the "Apply" button
    11. Zoom in on the central part of the sky, i.e. stuff near the zenith:
      In the "Sky View" window, drag the left slider upward about 1/4 of the way.
      Notice that you need to reset the "Deep Sky Lim Mag".
    12. Make a list of objects:
      For each green circle, move the pointer over the object and press and hold the right mouse button.
      Copy the of the object name down.
      This is best done in pairs: One to click, one to write the name down.
      Preferentially select objects closer to the zenith (the centre).
  2. Checking if they fit well on the CCD frame
    1. Start SkyCat:
      source /nfs/proto/jSky
      JSkyCat &
    2. Open the "Digitized Sky at STSci" window:
      Menu: Data-Servers -> Image Servers -> Digitized Sky at STSci
    3. Set the image size:
      Get the specifications for the CCD camera
      Change the width to 18.7
      Change the height to 12.6
    4. Search for an object:
      In the "Object Name:" window, enter the name of the object recorded earlier.
      Click on "Get Image".
      After a pause, an image will appear in the main SkyCat window.
      If a window displaying fits header information pops up as well, it may be safely closed.
    5. Review image:
      Decide if the galaxy will make a suitable target.
      Here are a few suggested criteria:
      • Does the galaxy fit nicely into the frame? Is it too small? too large? Is most of the galaxy outside the frame?
      • Is it aligned nearly face-on? Edge-on?
      • Does it fit project criteria?
    6. Record the RA & Dec:
      alpha and delta from the "Digitized Sky at STSci" window.
    7. Record an approximate galaxy classification.
    8. Repeat steps 2 to 7 for each of the objects.

After collecting information on a dozen or more objects, review the data and select the best candidates.

Now go observing!